Concept 5 of 6
Length Word Problems
Today's big idea
Joining lengths means add; cutting a piece off means subtract.
A 14 cm and a 9 cm ribbon tied make 23 cm.
How it works
👀 What's going on?
Two ribbons tied together, or one cut shorter. Do you add or take away?
💡 Here's the trick
Joining lengths means add; cutting a piece off means subtract. Keep both in the same unit.
A 14 cm ribbon tied to a 9 cm ribbon: 14 + 9 = 23 cm.
✍️ Try it
A 20 cm string with 7 cm cut off. How long now? → 13 cm.
⚠️ Watch out
Both lengths must be in the same unit before you add or subtract.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“A string is 18 cm. You cut 5 cm off. How long now?”
- 1
Cut means subtract
Cutting a piece off means subtract.
- 2
Do the subtraction
18 − 5 = 13
- 3
Answer ✓
13 cm
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Read the clue: tied together.
A 14 cm ribbon is tied to a 9 cm ribbon.
Does this add or subtract?
Quick check
✅ VERIFICATION
A rope is 25 cm. You tie a 15 cm piece to it. How long is it now?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Line Plots
One X for each length; count the Xs.